1. Field of the Invention
The present invention relates to a control device for a vehicle alternator, particularly a device for controlling supply of the field current of the alternator according to operation conditions of the alternator.
2. Description of the Related Art
In an alternator disclosed in JP-A6-276796, field current is supplied when output voltage generated due to remanent magnetism of the rotor core is detected by a voltage detecting circuit. In an alternator disclosed in JP-A-8-205497 a plurality of permanent magnets are fixed to the rotor core to provide such output voltage to be detected by a voltage detecting circuit for supplying the field coil with field current.
However, both voltage detecting circuits disclosed in above publications are powered by a vehicle battery. Therefore, the voltage detecting circuits operate even when the alternator does not operate and, accordingly, unnecessary current is always supplied from the battery. This deteriorates the battery and the engine starting performance. In addition, if such a circuit happens to be exposed to salt water or muddy water, leak current may flow from the battery to the output terminal of the alternator. This causes the voltage detecting circuit to erroneously allow supplying the field coil with current. This results in abnormal discharge of the battery.